Re: [PATCH] receive-pack, fetch-pack: reject bogus pack that records objects twice

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 18, 2011, 19:22 UTC
Message-ID: <7v62ihkzhb.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20111118184455.GA13782@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 11 quoted lines

> On Fri, Nov 18, 2011 at 10:41:35AM -0800, Junio C Hamano wrote:
>
>> Jeff King <peff@peff.net> writes:
>> 
>> > If we are fixing a thin pack (which should be the case most of the
>> > time), we are rewriting the packfile anyway. Shouldn't we just omit
>> > the duplicate?
>> ...
> ... But I guess there is some complexity
> with deltified entries? As in, if the first entry is deltified but the
> second is not, you would want to keep the second one?

I think you answered your own question here; it is not "some complexity" but is exactly the "you need to memmove() in the output file" situation in the message you are responding to.

Upon seeing a delta, you would not know if the same object as this delta represents appears later in the pack stream, which means until you read to the end you wouldn't know. You obviously would not want to hold onto all deltas in-core to "just omit the duplicate".